Building Statistics II - Building Systems
The delivery method for the Phoenixville Area Middle School was multiple prime design-bid-build with an agency construction manager. There are a total of seven prime contracts on the project: general trades, electrical, HVAC, fire suppression, plumbing, roofing and food service. IMC Construction, the general trades contractor, had the largest volume of work and was responsible for on-site coordination. Construction began with the gymnasium area, and progressed along through the classroom areas to finish with the auditorium.
The PECO primary overhead electric line enters the middle school at the South-western corner of the building. Here it encounters four transformers serving different areas. The ratings of these transformers are 500 KVA, 300 KVA, 300 KVA, and 150 KVA. The primary voltages are 480 V, with a secondary voltage of 208/120 V, 3 phases and 4 wires. These transformers distribute power to the entire building. A 230 KW diesel driven backup generator operates at 480/ 277 V, with 3 phases and four wires. In the event of power failure, this begins operating and ensures the critical safety systems of the building stay online.
The lighting system is typically comprised of fluorescent fixtures. LED lights are used in the auditorium to light the aisles, and fixtures with dimming capabilities allow for different styles to be achieved. Occupancy sensors control each room to prevent wasted energy when spaces are not occupied.
The mechanical system utilizes water source heat pumps throughout the middle school to efficiently regulate the indoor environment. Two large water source heat pumps operate on the roof, serving the administration room and media center. Nine different console water source heat pumps serve larger rooms and stairwells. A total of 78 smaller scale water source heat pumps serve individual rooms. Four rooftop heat recovery units operate on the rooftop. Variable air volume boxes and individual room controls allow each classroom to achieve the desired climate.
Cooling is provided with closed circuit cooling towers and fifteen split air conditioning units. Heating is provided by three gas powered condensing heaters, along with electric units throughout the building. The ductwork on the roof is specified as McGill rectangular galvanized duct with 1 ½” fiberglass liner and perforated inner line. Elbows are mitered with double thickness vanes. They are insulated with 2” rigid insulation. They are weatherproofed with white EPDM roofing.
The Phoenixville Area Middle School rests on a shallow reinforced concrete foundation. The spread footings, piers, and slab on grade have a 28 day compressive strength requirement ranging from 3000 – 4000 psi. The spread footings for the masonry walls typically are 2’ 8” wide by 1’ 0” deep, and are reinforced with #4 and #5 rebar. The foundation slab on grade is 4” thick, and rests on 6” of stone drainage fill. A vapor retarder rests above the stone, and it is reinforced with 6 x6 – W2.9x2.9 WWF. Vertical crack and construction joints are specified at no more than 30’ apart.
The superstructure is composed of steel framing, composite metal decking, and concrete masonry sheer walls. Typical steel columns are hollow structural steel members dimensioned at 8” x 8” x 3/8”, conforming to ASTM A36 code. Some areas have slightly different dimensions for the HSS columns or are designed with a wide flange beam. The metal decking is supported by a web of varying size wide flange steel beams conforming to ASTM A992. Roofs in areas such as the gymnasium and auditorium are supported by custom barrel trusses made of steel members. Steel members typically are joined by bolted shear connections; however some welding is done for certain members.
The floors are 2” – 20 GA composite metal deck with a 3 ½” concrete topping reinforced with 6 x 6 – W2.1 WWF, with a total thickness of 5 ½”. The decking is designed for 3 span condition un-shored construction. The decking is welded to a bent plate at columns. In general, the roof metal decking is 1 ½” 20 GA galvanized acoustic metal rood deck, the be finished with paint. The concrete slab on deck has a strength requirement of 3500 psi. It is a normal weight concrete reinforced with WWF. The contractors used pumping equipment to get the concrete to the upper levels of the building. There it was manually leveled off to the uniform thickness specified. Running electrical conduit through the slab on deck is not permitted.
Fire Protection (active, passive, construction type by code)
The fire protection system is a wet-pipe system conforming to NFPA 13 and IBC 2006. Each sprinkler head is not permitted to cover more than an area of 225 square feet.
An elevator is located towards the end of the area containing the classrooms. It is a Continental 50, 5000 lb. capacity model.
Six 4 in. communication conduits are installed off of the main line running along the northern boundary of the site. A sound system to be used for administrative announcements is to be located throughout the building. The auditorium by far contains the most speakers.